1. Field of the Invention
The present invention relates to a cassette type bubble memory device, hereinafter referred to simply as a "cassette memory".
Along with integrated circuit (IC) memories and floppy disks, bubble memory devices have come into increased use in recent years. Bubble memory devices have the advantages of: nonvolatile information storage, enabling easy rewriting; a solid chip construction without any mechanically movable parts, enhancing the reliability of the device; and small size and high density, enabling mounting the bubble memory devices on printed circuit boards. Such devices have been recently found to be particularly useful as file memories or program loaders in the field of numerical control (NC) machines, industrial robots, terminal units for manufacturing control point-of-sale (POS) systems, office automation (OA) machines, and so on.
In order to make such bubble memory devices easily transportable in the same manner as floppy disks or cassette tapes, a cassette memory in accordance with the invention comprises a bubble memory device accommodated in a case which can be inserted into a bubble memory control unit.
The cassette memory of the invention is small in size (thickness, width, and length) and light in weight so as to be easily carried by a person who operates these machines or units.
2. Description of the Prior Art
As well known in this field of art, a bubble memory device comprises a shield case of soft magnetic metal for accommodating therein a bubble memory chip, bias magnets, rectifiers, X and Y drive coils for generating a rotating magnetic field for driving bubbles, and, if applicable, release coils for erasing the information stored in the bubble chips.
As also well known, a memory system including a bubble memory device requires a direct peripheral circuit, also referred to as a "linear circuit", for directly driving and controlling the device with analog signals and an indirect peripheral circuit for controlling the direct peripheral circuit with digital signals of a transistor-transistor-logic (TTL) level in accordance with instructions for writing or reading of information from a host system.
The direct peripheral circuit includes a coil drive circuit for driving and controlling the bubble memory chips by supplying a predetermined current, i.e., analog signals, to the drive coils or memory chips, a function drive circuit, and a sense amplifying circuit for amplifying the sensed output voltage at a voltage level of a few mV from a detector in the bubble memory chips and converting in into TTL level.
The indirect peripheral circuit includes a bubble control circuit for controlling the drive of the bubble memory chips by inputting various control digital signals to the direct peripheral circuit in accordance with the instructions for writing or reading information from the host system and outputting the digital sensed signals from the direct pheripheral circuit (sense amplifier circuit) to the host system.
One prior art cassette memory, such as disclosed in Japanese Unexamined Utility Model Publications (Kokai) Nos. 56-56098 and 56-56099, is constructed with the bubble memory device and outside lead connector both mounted on a solid printed substrate (a printed substrate with no flexibility) and accommodated in a plastic or metal case. The printed substrate may be provided with a direct peripheral circuit (sense amplifier circuit) as well as the memory device. The cassette memory thus constructed can be detachably inserted into a receiving connector of a magnetic bubble memory control unit provided with direct and indirect peripheral circuits.
In this cassette memory, the printed substrate usually has a thickness of 0.8 to 1.6 mm. The lead terminals of the device are formed with a "stand off" so as to position the device about 1 mm above the printed substrate and thus improve soldering when dipping in solder. The total thickness of the known cassette memory, including the thickness of the printed substrate, the space between the device and the printed substrate, the height of the bubble device, and the thickness of the cassette case, is about 20 mm.
Another cassette memory has been proposed wherein a printed substrate is formed with an opening. The bubble memory device is situated within the opening to obtain a thin cassette memory having a thickness of about 10 mm. In this case, however, the printed substrate has to horizontally extend from the peripheral edges of the device.